As fitness-tracking bracelets go mainstream, style mavens are exercising their right to be geeky and fashionable

"MISSED-STEP REGRET" is an affliction that can befall the data-obsessed when they opt not to put on their fitness-tracking bracelets, those wearable gadgets—like the Fitbit Flex, Jawbone UP and Nike FuelBand—that count the number of steps taken in a day.

It happened recently to Pati Dubroff, 45, a makeup artist in New York and Los Angeles who works with Miley Cyrus, Natalie Portman and Charlize Theron. Since she began to wear a black Jawbone UP24 bracelet two months ago, Ms. Dubroff has loved tracking her every...